Hypothetical question

[GH1]

If I have a .45 ACP that travels around 1000 fps in a handgun, approximately what velocity can I expect fom a carbine with an 18" barrel?
GH1

[kynardsj]

According to what powder they're loaded with I would guestimate 1200-1300 fps hypothetically guestimating.

[Sweetwater]

I dont' have access to my software right now (not on this computer) but I offer for hypothetical comparison, a couple of similar comparisons. A lot will depend on your selection of powder. If you are using a powder fast enough to completely burn in your autoloader or revolver, there will be small gain. However, if you are using a slower burner, some real gain will be gotten.
For comparison, my reduced load in my 41Mag;
Bullet weight 215gr with small charge of Green Dot 933fps in 4 5/8" Ruger Blackhawk vs 1115fps in 20" Marlin

and a heavier charge in my 41Mag;
Bullet weight 225gr with heavy charge of W296 - 1190fps in 4 5/8"" Ruger Blackhawk vs 1680fps in 20" Marlin

These are cast bullets chrony'd at 10ft from the muzzle. I expect you are using powder on the fast end of the spectrun,, so I would expect you to see 200-300 fps gain in the carbine. This is a LOT of speculation.

Regards,
Sweetwater

[gray-wolf]

Until we get an expert opinion on this I would venture to say, if the 45 has a 5" barrel and the carbine has a 18" barrel---and the bullet velocity is 1,000 FPS or lower.  The increase in Vel. would be 10 FPS
or 10X13=130 FPS increase or 1,130 FPS.
  But there are many other things to take into consideration. So I look at this as a rule of thumb answer on my part.
  I remember Chuck Hawks saying once that: up to 1,000 FPS = 10 FPS gain per inch of barrel.
  Up to 2,000 FPS = 20 FPS gain per inch of barrel.
   "   "  3,000   "   = 30  "      "     "    "     "    " 
I do think powder burn rate will enter into the equation Plus a lot more.
A good question for us not degreed in ballistic science.
We should have a prize for the correct answer.

Any one have an exact formula ?

GW.   

[Grumulkin]

I would assume that the handgun in question has a barrel between 4 and 6 inches long.  Velocity loss or gain per inch of barrel change will be more for barrel lengths below 18 or 19 inches.  Below 18 or 19 inches the velocity change per inch of barrel will likely be in the 25 fps range while above that it will probably be in the 15 fps range.

Other than an educated guess from previous studies in which barrels were progressively shortened and the velocity checked, it's impossible to say exactly without actually shooting the respective barrel lengths.  Also, even in barrels of exactly the same length there can easily be 100 fps differences in velocities with exactly the same ammo when shot in different firearms.

[rg1]

 Check out the results at this site:
http://www.ballisticsbytheinch.com/results.html

[Graybeard]

I'd not automatically assume any increase. Ya might or ya might not get an increase. Small case rounds like that can actually lose velocity if the barrel gets too long. It's about expansion ratio.

I don't know the answer but with an expansion ratio like it has it won't be much if any increase I'd hazard a guess.

[GH1]

Thanks for all the replies everyone.  This question came up from a coworker who is considering getting a .45 carbine to go with his 1911.  He doesn't reload so he can't take advantage of a slower burning powder.  I realize I didn't offer much info such as bullet weight, pistol barrel length, etc., but I thought I'd throw it out there anyway. 
Thanks again.
GH1

[Grumulkin]

I'd not automatically assume any increase. Ya might or ya might not get an increase. Small case rounds like that can actually lose velocity if the barrel gets too long. It's about expansion ratio.

I don't know the answer but with an expansion ratio like it has it won't be much if any increase I'd hazard a guess.

The 22 LR will increase in velocity up to about 18 inches of barrel length after which it decreases.  I suspect a 45 Auto would be similar.